The rate of consumption of oxygen by V-79 cells in multicellular spheroids was measured as a function of the spheroid diameter. In situ consumption was equal to that of exponentially growing cells for spheroids less than 200 micron in diameter. The rate of oxygen consumption decreased for cells in spheroids between 200 and 400 micron diameter to a value one-fourth the initial, then remained constant with further spheroid growth. Comparison of consumption rates for spheroid-derived cells before and after dissociation from the spheroid structure indicated that the spheroid microenvironment accounted for only 20% of the change in oxygen consumption rate. Cell-cell contact, cell packing, and cell volume were not critical parameters. Plateau-phase cells had a fivefold lower rate of oxygen consumption than exponential cells, and it is postulated that the spheroid quiescent cell population accounts for a large part of the intrinsic alteration in oxygen consumption of cells in spheroids. Some other mechanism must be involved in the regulation of cellular oxygen consumption in V-79 spheroids to account for the remainder of the reduction observed in this system.
Yeast cells grown ailaerobically on glucose suppleillented with yeast extract, hydrolyzed casein, and oleic acid developed a respiratory capacity on exposure to air. 'The time course of development of respiration was characteristic with an abrupt onset of oxygen consumption. The magnitude of the uptake of oqrgen and the kinetics of its onset were determined by the concentration of glucose to which the yeast was exposed during growth and by the relative amounts of glucose and yeast present during the time of adaptation. A source of amino acids was necessary during the time of adaptatioil for the consistent development of respiration. Under the growth conditions used, adaptive developlllent of respiration occurred 111ost efficieiltly when the cells were harvested immediately prior to the onset of the stationary phase. C>'tochrome oxidase was virtually absent fro111 the anaerobically grown cells. The liinetics of its adaptive formation were not the same a s those for the development of respiration. Cytochrome oxidase appearecl before respiratioil became appreciable. ii'hen these anaerobically grown >,east cells were added to the adaptation n~ediuill there was a burst of gas output. 'The identity of the gas is un1;nown but it is likely to be COs, HZS, or Hs. 'I'he role of glucose and other factors in the adaptive development of respiration in yeast is discussecl.
This paper describes the aerobic behaviour of yeast, previously grown anaerobically on a number of different carbon sources. The results show that yeast grown anaerobically on galactose retains its respiratory activity whereas the yeast grown similarly on glucose loses it. METHODS Maintenance and growth of yeast. Saccharomyces cere-Vi8siae strain no. 77 of the National Collection of Yeast Cultures (Brewing Industry Research Foundation, Nutfield, Surrey) was used in the present work. The organism was maintained aerobically on agar slopes containing inorganic salts, 2-25% (w/v) of Difco malt extract, 0.05% of Difco yeast extract and 0 5% of sucrose. The yeast was grown for 48 hr. at 300 and subcultured monthly. Growth of anaerobic cels8. The medium for the anaerobic bulk growth of the yeast contained (per 1.): glucose, 20 g.;
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